(1) Field of the Invention
The present invention relates to an olefinic rubber composition. More specifically, the present invention relates to a thermoplastic olefinic rubber composition, which is superior in appearance, oil resistance, mechanical strength and vacuum-forming moldability.
(2) Description of the Related Art
A thermoplastic elastomer composition obtained by so-called dynamic vulcanization is already known in the art, and extensively applied for uses such as car parts. According to the dynamic vulcanization, a rubber like polymer such as a radical vulcanizable olefinic elastomer and a non-radical vulcanizable olefinic resin such as polypropylene (PP) are vulcanized with each other through melt-kneading in the presence of a radical initiator in an extruder.
As such an olefin elastomer, ethylene-propylene-non-conjugated diene rubber (EPDM) and a thermoplastic elastomer composition produced with use of a metallocene catalyst (JP-A-8-120127 and JP-A-9-137001) are known. However, the above-mentioned compositions are high in their cross-linking level, and therefore the compositions are not always sufficient in appearance and vacuum-forming moldability in spite of superiority in their mechanical strength and oil resistance. Further, a rheology-modified thermoplastic elastomer composition obtained by vulcanization an ethylene-α-olefin copolymer and a high melting polymer with the aid of a peroxide is disclosed (WO98/32795). However, the composition is low in its cross-linking level, and therefore the composition is inferior in mechanical strength and oil resistance in spite of superiority in its appearance. Accordingly, a thermoplastic olefinic rubber composition sufficient to practical application has been desired.